Modulation



Dec. 12, 1933.

N. E. LINDENBLAD MODULATION Filed March 27, 1931 2 Sheets-Sheet l 400/0 25 AMPl/F/ER 10 M J2EE? INVENTOR N.E. LINDENB '17 BY M ATTORNEY Dec. 12, 1933.

Filed March 27, 1931 2 Sheets-Sheet 2 M 400/0 AMPu/VE/P ill! 34 :E/ M 3: 400/0 35 5E AM/Z/fii'r? INVENTOR N E LINDENDLAD BY m ATTORNEY Patented Dec. 12, 1933 ldtiDULATEEON Nils E. Lindenblad, Zort Jeiierson, N. ZZZ, as

signer to Radio Corporation of Ernerica,

pcration of Delaware PAIEN? Ol- FICE a cor= Application 2%, $331. No. 525333 Claims.

This invention has as an object the provision of new and useful methods and means for modurating high frequency undulatory electrical energy.

Ultra short Wave length undulatory electrical energy has been produced by maintaining the control electrode of an electron discharge device at a relatively high, positive potential with respect to the other electrodes of the device. Oscillation generation may then be attributed to the fact that electrons, attracted to the control electrode from the electron emitting cathode, travel through the spaces of the grid only to be reattracted after they have passed the grid or control electrode and approach the anode, by the strong attracting potential on the control electrode. The electrons may have their return to the control electrode hastened by the action of a negative charge imparted to an electrode on the far side of the control electrode away from the cathode, which far sided electrode normally an anode, may be, if desired, made in the form of an electron emitting body similar to the cathode. The returning electrons again pass through the interstices of the grid only to approach the oathode, where they are forced to return towards the grid again, repeating the cycle outlined, by virtue of the combined attractive action of the grid and the repelling action of the space charge about the cathode.

Oscillators such as described may be made of a single electron discharge device or may be constructed out of electron discharge devices arranged in pushpull fashion.

A further object of the present invention is to provide means for the modulation of the oscillatory energy generated in the fashion described. To do so, it is a further object of this invention to provide means for varying, in accordance-With modulating energy, either control electrode potential or anode potential of the electron discharge device or devices, as the case may be, forming the ultra-short-wave length oscillation generator.

For control electrode or grid modulation, it is a further object of this invention to provide a substantially unidirectional source of potential having its positive terminal connected through an impedor to the control electrode or electrodes, and, a modulating tube supplied with modulating energy having its output circuit or output electrode connected to a point between the impedor and control electrodes for eifecting the desired modulation of the oscillations generated by the oscillator.

Variation in anode or control electrode potentials for the purpose of obtaining modulation, however, involves both the amplitude and frequency modulation of the oscillations generated. As it is desirable to have one form of modulation so or the other, that is to say, either amplitude modulation or frequency modulation to the exclusion of the other, a further object of the present invention is to provide a method and means for eliminating at will, either the frequency modulation component or the amplitude modulation component of the modulated oscillatory energy.

To fulfill the foregoing object, there is applied, according to the present invention, in a balancing sense, in addition to the modulation potentials applied to the electrode or electrodes of the oscillator, modulating potentials to a plurality of different electrodes of the oscillator. By proper choice of the potentials applied in a baiancing sense, simultaneously to the electrodes, either the amplitude or frequency components may be balanced out in the circuits of the oscillator. leaving in the output circuit of the oscillator the desired modulation component.

A further object of the present invention is to 30 provide apparatus for carrying out the foregoing method, and, according to this invention, it preferably takes the form of a potentiometer to which are supplied modulation potentials. Then, by suitable taps from the electrodes of the oscil- 35 lator to the potentiometer the desired compensating, simultaneously applied voltages may be obtained.

While the circuits briefly described hereinabove may theoretically be balanced by action of the 9g potentiometer alone, it will be found in actual practice that usually the anode circuit of the oscillator has, by virtue of the sources of potential therein, large capacitance to ground which acts as a shunting capacitor for the modulating frequencies, destroying what would otherwise be perfect potentiometer adjustment. A further object of the present invention is to remedy this defect and this is accomplished by shunting across a portion of the potentiometer a capacitor which will neutralize the, referred to, capacitance to ground of certain of the oscillator circuits.

Although the present invention is defined in the appended claims, it may best be understood both as to its method of operation and construction by referring to the accompanying drawings, which, it is to be clearly understood, are not to be considered in any way aslimiting the invention. In, the drawings,

Fig re 1 illustrates in diagrammatic form an frequencies.

ultra-short-wave length oscillation generator, and means for modulating the oscillations generated thereby by variation in anode potential of the oscillator,

Figure 2 illustrates a similar system wherein modulation is accomplished by variation in control electrode or grid potential,

Figure 3 illustrates an oscillatory system, having means for modulating the oscillations generated thereby together with means for removing either the frequency or amplitude component as desired, of the modulated oscillation, and,

Figure 4 illustrates apparatus for eliminating either the frequency or the amplitude modulation component of a modulated'regeneratively connected oscillator.

Figure 1 illustrates an ultra-short-wave length transmitting system comprising an oscillator 0 formed of a pair of electron discharge devices 2, 4, whose anodes are connected together in pushpull fashion by means of a metallic U-shaped slide or trombone slide 8 to which is coupled an antenna 10 through a suitable transmission line 12 and blocking condensers 14. Anode potential, preferably of a small negative value, is supplied from a potentiometer 16 to a voltage nodal point 18 in the anode circuit 8; and, the positive terminal of a substantially unidirectional source 20 is coupled to a voltage nodal point 22 in a control electrode circuit 6, similar in construction to anode circuit 8.

For modulation, modulating energy from source M is amplified by a suitable amplifier 24 and fed through transformer 26 and potentiometer 16 to the anodes of electron discharge devices 2 and 4, causing modulation of the ultrashort-wave length energy generated by the oscillator.

The ultra-short-wave length energy is, as already indicated, generated by virtue of the fact that electrons attracted towards the grids, pass therethrough and upon approaching the negatively charged anodes or plates are repelled by the anodes, reattracted by the grids only, after repassing therethrough, to approach the repelling space charge of the cathodes where they are again reattracted towards the control electrodes to repeat the cycle outlined.

By making the anode and control electrode circuits each substantially an odd number of half wave lengths long, the tubes 2, 4 for ultrashort-wave length oscillation generation will act in pushpull fashion.

Oscillations generated with an oscillatorof the type shown in Figure 1, may be modulated by variation in the unidirectional grid or control electrode potential at modulation frequencies. Such a system is shown in Figure 2 wherein unidirectional positive potential from source 20 is applied through an impedor in the form of a choke coil 28 to the control electrodes of oscillator tubes 2, 4. Amplified modulating energy from source M is applied to one or more paralleled modulator tubes 30. As illustrated the output electrodes or circuits of modulator tubes 30 are connected to a point 32 between impedor 28 and the electrodes to which source 20 is coupled; or in other words, to a point 32 on the side of choke coil 28 away from potential source 20. If desired, the output of source 24 may be made, in any of a number of known ways, a relatively low radio frequency potential modulated at signal In that case, antenna 10 will radiate a double modulated wave.

In either of the modulating schemes shown in Figures 1 and 2, there will appear in the output circuit of the oscillator both frequency modulated as well as amplitude modulated oscillations. It is often desirable to eliminate one of the modulated components such as, for example, the frequency component. To do this, according to the present invention, a scheme such as shown in Figure 3 is resorted to. form of a resistor 34 is coupled between the far end of impedor 28 and ground. As a result of the connection of resistor 34, modulating potentials appear thereacross, and, by the proper choice of connection 36, coupling'the anode electrodes of electron discharge devices 2, 4, to resistor 34,

modulation voltages in a balancing sense may be' applied simultaneously to both the control electrodes and anodes of electron discharge devices 2, 4. By suitable adjustment of tapping point 38 on resistor 34, the frequency component appearing in the output circuit 40, here inductively coupled to the anode tuning circuit, may be eliminated.

The elimination may be ascribed to the fact that the frequency of the oscillator may be varied by variation in plate potential. Then, the oscillator may be brought back to its initial frequency by varying the grid potential. The resulting curves, showing the relationship between the anode and control electrode potentials for the generation of constant frequency ultrashort-wave length energy, will be found to be substantially flat or almost a straight line in the region in which it is desired to utilize the oscillator. Consequently, by the application of similar and balancing potentials, or modulating potentials, or modulation potentials of balancing sense to various electrodes of the oscillator, the frequency component may be eliminated.

Similarly, it will be found that by suitable adjustment of tapping point 38 the amplitude modulation component may be eliminated giving pure frequency modulated energy in the output circuit of the oscillator.

In the event that there is a ripple in the unidirectional supply source as where it is obtained from a rectifier, the ripple may be removed by another adjustment of tap 38. This action is claimed and described in the copending application of Bernard Salzberg, Serial Number 505,- 488, filed December 30, 1930. (RCA docket 4871) At the high frequencies involved, the capacity An impedor in theto ground, of the various elements in the anode circuit such as resistor 17, potential source 19 of potentiometer 16 together with the various connecting leads such as conductor 36, will act as l a shunting capacity the effects of which cannot be eliminated by adjustment of tap 38. To remove this defect, a capacitor in the form of a variable condenser 42 is connected across a portion of resistor 34 or, between tapping point 38 and a point between impedor 28 and electrodes 23 the condenser being of suitable value to neutralize the effect of the capacity to ground, indi cated in dotted lines by capacitor 44, of the anode circuits. In actual practice, it was found that for desired operation, in order to eliminate frequency modulation, the variation in grid voltage required was about three and one-half times the variation in plate voltage which, of course, would indicate that the portion of resistor 34 included between tapping point 38 and point 32 should be three and one-half times that included between tapping point 38 and ground. For the capacity neutralization of the ground capacitor 44, it will be found that the values of capacity Zoe:

should be chosen in approximately inverse sense, in which case capacitor 42 should be made approximately one-third that of the capacitance to ground.

In order to lessen the flow of energy through impedor or resistor 34, as well as to increase the ease of applying suitable unidirectional potentials to the anodes of the oscillator, a source of potential 46 as illustrated, should be placed in series with resistor 34 to balance out the steady direct current voltage drop in said resistor.

It should be clearly understood, that in addition to the ordinary modulation applied to an electron discharge device, the idea of simultaneous modulation of a plurality of electrodes of the electron discharge device for the purpose of having the simullaneous potentials balance the effect of a certain type of modulation resulting from the ordinary modulation, may not only be applied to the oscillators of the type described, but may in general be applied to any modulation system.

For example, application of the described scheme for the elimination of say, frequency modulation in a modulated regeneratively connected oscillator, is shown in Figure 4. Electron discharge device oscillator 50, regeneratively con nected through the action of feed back coil 52, feeds the generated oscillations into a power amplifier 54 which in turn feeds them to a suitable transmission line 56 to a radiating antenna 58. Application of amplified modulation energy from a source 60 to modulator tube 62 coupled to the anode circuit of oscillator 50 causes modulation of the oscillations generated by the oscillator 50 both in frequency and in amplitude.

In order to eliminate one of the undesired modulation components, a resistor 64, in series with a source of potential 66, is coupled between ground and the far end of choke coil 68 in the anode supply lead for oscillator 50. By virtue of conduc'or 70, simultaneously acting modulation potentials may be applied to the control electrode and anode of oscillator 50 of suitable values so as to eliminate the undesired component.

In the event that the tapping point of conductor 70 on resistor 64 does not give a desired control electrode biasing potential for the control electrode of oscillator 50, a capacitor '72 may be inserled in conductor '70 which capacitor is of a value ofiering no appreciable impedance to modulation energy but, of course, effectively blocks the application of unidirectional potentials, from resistor 70, to the control electrode or grid of oscillator 50. A suitable grid biasing potential may then be applied through a conductor 74 connected to conductor 70. Depending upon what balance is desired it may sometimes be necessary to reverse or regulate the phase of the potential obtained at the tapping point. This can be done by means of transformers or other suitable devices.

Having thus described my invention, what I claim is:

1. In a transmitting system, transmitting modulated carrier energy, having an electron discharge device subjected to both carrier energy and modulating energy in whose output circuit there appears both frequency and amplitude components of the carrier energy, the components resulting from the modulation, the method of eliminating one of the components which includes simultaneously applying in balancing sense modulating potentials to a pair of electrodes of the device whereby elimination of the undesired component ensues.

2. In a transmitting system, transmitting modulated carrier energy, having an electron discharge device, subjected to both carrier energy and modulating energy, in whose output circuit there appears both frequency and amplitude components of the carrier energy, the components resulting from the modulation. the method of eliminating the frequency component which includes simulianeously applying in balancing sense modulating potentials to a pair of electrodes of the device whereby elimination of the frequency component ensues.

3. In a transmitting system, transmitting modulated carrier. energy, having an elec.ron discharge device, subjected to both carrier energy and modulating energy, in whose output circuit there appears both frequency and amplitude components of the carrier energy, the components resulting from the modula.ion, the method of eliminating one of the components which includes simultaneously applying, in balancing sense modulating potentials to the anode and a grid of the device whereby elimination of the undesired component ensues.

4. In a transmLting system, transmitting modulated carrier energy, having an electron discharge device, subjected to both carrier energy and modulating energy, in whose output circuit there appears both frequency and amplitude components of the carrier energy, the componen s resulting from the modulation, the method of eliminating the frequency component which includes simultaneously applying in balancing sense modulating potentials to the anode and a grid of the device whereby elimination of the frequency component ensues.

5. In apparatus for undulatory energy, an electron discharge device oscillator, means for modulating oscillations produced thereby, an impedor, means for subjecting the impedor to modulating potentials, and connections from the impedor to electrodes of the oscillator for applying thereto modulating potentials for canceling a predetermined undesired component in the output of said oscillator.

6. In apparatus for undulatory electrical energy, an electron discharge device having an anode a cathode and a control electrode, a source of constant potential, an impedor coupling said source and the control electrode of said device, another electron discharge device having modu lating potentials supplied thereto having its output circuit coupled to a point between the impedor and the conthrol electrode, a resistor between said connecting point and ground, and, a connection from the anode of said first mentioned device to a point on said resistor.

' 7. In apparatus for undulatory electrical energy, an electron discharge device having an anode, a cathode and a control electrode, a source of constant potential, an impedor coupling said source and the control electrode of said device, another electron discharge device having modulating potentials supplied thereto having its output circuit coupled to a point between the impedor and'the control electrode, a resistor coupled between said coupling point and ground, a connection from the anode of said first mentioned device to a point on said resistor, the point on said resistor being so chosen that modulating potentials are simultaneously applied to the control electrode and anode of said first mentioned electron discharge device of values to eliminate ISO iii)

frequency modulation of high frequency energy to which said first mentioned electron discharge device is subjected.

8. In apparatus for undulatory electrical energy, an electron discharge device having an anode, a cathode and a control electrode, a source of constant potential, an impedor coupling said source and the control electrode of said device, another electron discharge device having modulating potentials supplied thereto having its output circuit coupled to a point between the impedor and the control electrode, a resistor coupled between said coupling point and ground, a connection from the anode of said device to a point on said resistor, and, a capacitor connected between the control electrode and anode of said first mentioned electron discharge device.

9. In apparatus for undulatory electrical energy, an electron discharge device having an anode, a cathode and a control electrode, a source of constant potential, an impedor coupling said source and the control electrode of said device, another electron discharge device having modulating potentials supplied thereto having its output circuit coupled to a point between the impedor and the control electrode, a resistor coupled between said coupling point and ground, a connection from the anode of said device to a point on said resistor, and a variable capacitor connected between the connection point between said impedor and the control electrode of said first mentioned device and the anode of said device, the capacitance value of the capacitor being so chosen that it neutralizes the effect of the capacitance of the anode circuit connections to ground.

10. In apparatus for undulatory electrical energy, an electron discharge device having an anode, a cathode and a control electrode, a source of substantially undirectional potential connected through an impedor between ground and one or" the electrodes of said electron discharge device, another impedor and a source of potential in series connected between ground and a point between said first mentioned impedor and the electrode to which it connects said first mentioned source of potential, a modulating tube having an output electrode coupled to a point between said first mentioned impedor and said first mentioned electrode, and, a connection between another electrode of said first mentioned electron discharge device and said second mentioned impedor.

11. In apparatus for undulatory electrical energy, an electron discharge device having an anode a cathode and a control electrode, a source of potential, an impedor coupling said source and one of the electrodes of said electron discharge device. a resistor and another source of potential in series connected between ground and a point between said impedor and said electrode, a connection from said resistor to another electrode of said device, and, a modulating tube having an output electrode connected to the point between said impedor and said first mentioned electrode.

12. In apparatus for undulatory electrical currents, an electron discharge device having an anode, a cathode and a control electrode, a source of potential, a choke coil for coupling the positive terminal of said source to the control electrode of said device, a resistor and another source of potential in series connected between said choke coil and control electrode and ground, a connection between the anode of said device and a point intermediate the ends of said resistor, and, a modulating tube having its output electrode connected to the control electrode of said electron discharge device.

13. In apparatus for undulatory electrical currents, an electron discharge device having an anode a cathode and a control electrode, a source of potential, a choke coil for coupling the positive terminal of said source to the control electrode of said device, a resistor and another source of potential in series connected between said choke coil and control electrode and ground, a connection between the anode of said device and a point intermediate the ends of said resistor, a variable capacitor connected across the control electrode and anode of said electron discharge device, and, a modulating tube having its output electrode connected to the control electrode of said electron discharge device.

14. In apparatus for undulatory electrical energy, a pair of electron discharge devices each having an anode a cathode and a control elec trode, like electrodes of the devices being coupled together; means for supplying a substantially unidirectional potential to a pair of the electrodes, said means comprising a source of potential and an impedor in series; another irnpedor connected between said first mentioned impedor and the electrodes to which it is connected and ground; a connection from said last mentioned impedor to another pair of electrodes; and, a modulating tube having an output electrode connected to a point between said first mentioned impedor and said first mentioned pair of electrodes.

15. In apparatus for undulatory electrical energy, a pair of electron discharge devices each having an anode a cathode and a control electrode, like electrodes of the devices being coupled together; means for supplying a subs;antially unidirectional potential to a pair of the electrodes, said means comprising a source of potential and an impedor in series; another impedor connected between said first mentioned impedor and the electrodes to which it is con nected and ground; a connection from said last mentioned impedor to another pair of electrodes; a capacitor connected across a portion of said last mentioned impedor; and, a modulating tube having an output electrode connected to a point between said first mentioned impedor and said first mentioned pair of electrodes.

16. In apparatus for undulatory electrical energy, a pair of electron discharge devices each having an anode a cathode and a control electrode, like electrodes of the devices being coupled together; means for supplying a substantially unidirectional potential to a pair of the electrodes, said means comprising a source of potential and an impedor in series; another impedor connected between said first mentioned impedor and the electrodes to which it is connected and ground; a connection from said last mentioned impedor to another pair of electrodes; a capacitor connected across, and a source of potential in series with said last mentioned impedor; and, a modulating tube having an output electrode connected to a point between said first mentioned impedor and said first mentioned pair of electrodes.

17. In apparatus for undulatory electrical energy, a pair of electron discharge devices each having an anode a cathode and a control electrode, like electrodes of the devices being coupled together; means forsupplying a substantially unidirectional potential to a pair of the electrodes, said means comprising a source of potential and a choke coil in series, a resistor connected to the end of the choke coil away from the potential source and ground means for connecting the anodes of the pair of devices to the resistor; a source of potential in series with the resistor; a condenser connected across a portion of the resistor; and, a modulating tube having an output electrode connected to the end of the choke coil away from the source of potential to which it is connected.

18. In a transmitting system, transmitting modulated energy, having an electron discharge device, subjected to both carrier energy and modulating energy in whose output circuit there appears both frequency and amplitude components of the carrier energy, the components resulting from the modulation, the method of eliminating the amplitude component which includes simultaneously applying in balancing sense modulating potentials to a pair of electrodes of the device whereby eliminationof the amplitude component ensues.

19. In a transmitting system, transmitting modulated carrier energy, having an electron discharge device, subjected to both carrier energy and modulating energy, in whose output circuit there appear signal modulated components of the carrier energy of substantially constant amplitude, the components resulting from the modulation, the method of eliminating the frequency component which includes simultaneously applying in balancing sense modulating potentials to a pair of electrodes of the device whereby elimination of the frequency component is accomplished.

20. In a transmitting system, transmitting modulated carrier energy, having an electron discharge device, subjected to both carrier energy and modulating energy in whose output circuit there appears signal modulated components of.

the carrier energy of substantially constant amplitude, the components resulting from the modulation, the method of eliminating the frequency component which includes applying modulating potentials to an input electrode of said dis-v charge device, applying modulating potentials to an output electrode of said device, and varying l the amplitude of the components applied to said electrodes in a sense to eliminate the frequency component resulting from the modulation.

21. In signalling apparatus, a pair of thermionic discharge devices, each having electrodes including an anode, a cathode and a control electrode, conducting means of variable length for connecting said control electrodes together, conducting means of variable length for connecting said anodes together, a circuit for supplying similar negative potentials to the anode electrodes, a circuit for supplying similar positive potentials to the control electrodes, said circuit comprising, a source of potential and an impedance in series between said control electrodes and ground, a resistance connecting a terminal of said impedance to ground by way of a source of potential, and a circuit for connecting the anodes of said devices to a point on said resistance, said last named circuit including a portion of the circuit for supplying potentials to the anodes of said tubes.

22. In signalling apparatus, a pair of thermionic discharge devices, each having electrodes including an anode, a cathode and a grid like electrode, conductors of variable length for connecting said grid like electrodes together, conductors of variable length for connecting said anodes together, a circuit connected between said last named conductors and the cathodes of said tubes for supplying similar potentials to the anode electrodes of said tubes to maintain said anode electrodes at a different potential than the cathodes of said tubes, a circuit connected with said first named .conductors for supplying other similar potentials between the grid like electrodes and cathodes of said tubes, said last named poten-s tials maintaining said grid like electrodes more positive relative to the cathodes of said tubes than said first named similar potentials maintain said anodes relative to said cathodes, and an audio frequency circuit connected between said second named conductors and the cathodes of said tubes.

NILS E. LINDENBLAD. 

